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Battery Cut Off Charger Circuit Using a Single Relay

Battery Cut Off Charger Circuit Using a Single Relay

Amazed to hear this! Yep that’s actually possible, you would need only one relay and a handful of diodes to make a simplest one relay automatic battery charger circuit.

How it Works

The idea struck me while trying to design the easiest possible battery charger circuit for one my clients.



The concept is simple; just raise the operating or triggering voltage of the relay up to the optimal battery charging threshold voltage by dropping the required amount of supply voltage to the relay coil, with the help of series diodes.The idea may be understood from the following points:

Take an ordinary relay, measure its triggering voltage by carefully applying a variable voltage across its coil.Now suppose the triggering voltage of the particular relay was about 9 volts, and also assume you want to raise its voltage to 14 volts, which may be your 12 volt battery’s charging threshold voltage.

We know that a 1N4007 diode drops about 0.6 volts across it, so if we add sufficient number of diodes in series with the relay coil would hopefully pull its tripping or triggering voltage to about 14 volts.

That means, 14 – 9 = 5, we’ll require 5/0.5 = 10 diodes in series to achieve this rise in the triggering voltage of the relay.That’s pretty simple and interesting isn’t it?The rest may be done with the help of the shown diagram…..your simplest single relay automatic battery charger is ready.

SHARING IS CARING!

About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



14 thoughts on “Battery Cut Off Charger Circuit Using a Single Relay”



  1. yes relay starts to switch on and off. i have made this circuit.this is due to disconnection. it order to overcome this connect 14v dc to battery positive terminal not through the NC of relay.

  2. Sir, thank you for sharing your idea on this simple circuit.
    What components will be required if I need this same simple circuit to charge 48 volts battery made from 4 x 12. The battery AH is not important.

    anticipating your quick response

    Thank you once more

    • sorry this circuit is not recommended for a 48V battery because too many diodes will be required for the 48v operation …….moreover the design is not too accurate.

  3. Actually, I was wrong in acknowledging the zener idea, it won't work.

    It has to be done exactly as suggested in the diagram in the above article. 1N4007 or 1N4148 in series with the relay coil is the only correct way of doing it.

    • Actually, I was wrong in acknowledging the zener idea, it won't work

      It has to be done exactly as suggested in the diagram in the above article. 1N4007 or 1N4148 in series with the relay coil is the only correct way of doing it.



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